In communication networks, such as telecommunication networks, a call or a service often involves, on the one hand, a control plane or signalling plane and, on the other hand, a user plane. The control plane or signalling plane is in charge of establishing and managing a connection between two points on the network. The user plane or media plane is in charge of transporting the user data.
In this context, network operators often want to define and enforce a set of rules in the network. A set of rules constitutes policies. A policy framework for managing and enforcing these policies usually includes at least three elements, or functions: a policy repository for storing the policy rules which may be user-specific, a policy decision element, function or point, and a policy enforcement element, function or point. The purposes of a policy framework include controlling subscriber access to the networks and services.
A policy framework notably addresses the decisions as to whether the subscriber is entitled, or authorized, to enjoy a service, and whether the network can provide the service to the subscriber.
Policy and charging control architectures, such as, but not limited to, the architecture described in 3GPP TS 23.203, Technical Specification Group Services and System Aspects, Policy and charging control architecture (Release 8) (available on http://www.3gpp.org), integrate the policy and charging control.
Policy and Charging Control (PCC) architecture permits to integrate both policy and charging control, optimizing the information flow. The architecture that supports Policy and Charging Control functionality is shown in FIG. 1 and is in accordance with TS 23.203, which specifies the PCC functionality for Evolved 3GPP Packet Switched domain, including both 3GPP accesses (GERAN/UTRAN/E-UTRAN) and Non-3 GPP accesses. In the following, an explanation of the main elements of such architecture will be provided.
The Application Function (AF) is an element offering applications in which service is delivered in a different layer (i.e. transport layer) from the one the service has been requested (i.e. signaling layer), the control of IP bearer resources according to what has been negotiated. One example of an AF is the P-CSCF of the IM CN subsystem. The AF shall communicate with the PCRF to transfer dynamic session information (i.e. description of the media to be delivered in the transport layer). This communication is performed using the Rx interface. The information in the Rx interface is derived from the session information in the P-CSCF (e.g. SDP when SIP is used for signalling) and it mainly includes what is called media components. A media component is composed by a set of IP flows, each one described through a 5-tuple, the media type and bandwidth required.
The PCRF is the function that provides policy and charging control for the Media Components negotiated between the UE and the AF. For that purpose, the PCRF creates PCC rules based on the information received from the Rx interface. PCRF, depending on the user and the requested service, include charging and policy information along with the a set of IP filter information: each IP 5-tuple is composed of src and destination IP address and ports, and the protocol id above IP (TOP, UDP). The filters included in PCC rules define what is called Service Data Flows (SDF), i.e. data flows that are treated in the same way regarding policy and charging. This Service Data. Flows are installed in PCEF through the Gx interface.
The PCEF encompasses service data flow detection (based on the filters definitions included in the PCC rules), as well as online and offline charging interactions (not described here) and policy enforcement. Since the PCEF is the one handling the bearers, this is where the QoS is being enforced for the bearer according to the QoS information coming from the PCRF. This functional entity is located at the Gateway (e.g. GGSN in the GPRS case, and PDG in the WLAN case).
In the PCC architecture, the policy control includes the QoS control. The PCEF enforces the authorized QoS for an IP-CAN bearer according to the information received via the Gx interface and depending on the bearer establishment mode. The enforcement of the authorized QoS of the IP-CAN bearer may lead to a downgrading or upgrading of the requested bearer QoS by the PCEF as part of a UE-initiated IP-CAN bearer establishment or modification. Alternatively, the enforcement of the authorised QoS may, depending on operator policy and network capabilities, lead to network initiated IP-CAN bearer establishment or modification. If the PCRF provides authorized QoS for both, the IP-CAN bearer and PCC rule(s), the enforcement of authorized QoS of the individual PCC rules shall take place first.
At IP-CAN session establishment or modification, the PCEF requests the policy rules to the PCRF. In the case that due to the size of the network, several PCRFs are deployed in different sites, the standard defines the DRA functional entity.
The DRA functional entity is defined in the 3GPP standards for PCRF discovery procedures where more than one PCRF is present in an operator's network. It proposes to use Diameter routing procedures using the NAI domain part. This solution assumes that the operator deployment uses one realm per site and that the NAI is used in the network.
Routing of Diameter messages from a network element towards the right Diameter realm in a PLMN is based on standard Diameter realm-based routing, as specified in IETF RFC 3588 using the UE-NAT domain part.
The DRA is defined in 3GPP to support the functionality of a proxy agent and a redirect agent as defined in RFC 3588.
Big operators offering services within large sized countries or having operations in several countries often divide their network in several sites. Each site is made up of the resources as a complete network, i.e. those types of network element and applications needed to provide the required services or at least one service. Each site provides service for the subscribers located as home or as visitor in the geographical area assigned to the site. The networks distributed in several sites are known as multi-site networks. The user identity used in the operator network is typically the MSISDN for traffic purposes; although in some cases may also be the IMSI or the NAI.
In this multi-site scenario, each PCRF contains subscription information of only the home subscribers. When a user is in a visited site, the control information relating to the traffic is routed through the visited PCEF. The visited PCEF routes the control information to the visited PCRF. As the visited PCRF does not have the subscription information of the visitor users, the PCRF needs to find the PCRF where the subscription information is stored. The solution proposed in the standard is based on the Diameter routing based on the realm, but this solution requires that the NAI is used; it is not valid when other types of subscriber identities are used, such is MSISDN. In addition it imposes requirements in the deployment of the network, i.e. one realm per each site, which is not always the case.
It is therefore desirable to provide methods, network entities, system and computer programs improving policy and charging control architectures and implementations in particular in multi site networks.